Electric incandescent lamp and manufacture thereof



May 24, 1966 EDWARDS ETAL 3,253,179

ELECTRIC INCANDESCENT LAMP AND MANUFACTURE THEREOF Filed Nov. 26, 1962 Invavtors: Geofige J. Edwards WiLLiam 6. James b flat/' Their- A t rneg United States Patent 3,253,179 ELECTRIC INCANDESCENT LAMP AND MANUFACTURE THEREOF George J. Edwards, Painesville, and William G. James,

Cleveland Heights, Ohio, assignors to General Electric Company, a corporation of New York Filed Nov. 26, 1962, Ser. No. 239,976 3 Claims. (Cl. 313-318) This invention relates to electric incandescent lamps generally and more particularly to structures and methods of assembly for protecting against damage due to arcing.

Incandescent lamps for general lighting purposes comprise a glass bulb having a neck portion with a reentrant glass stem sealed thereo, a filament in the bulb, a pair of lead-in wires connected to respective ends of the filament and extending through a press seal portion at the inner end of said stem and through the interior of the stem to respective contact terminals of a hollow shell base attached by cement to the bulb neck. The outer end portion of one of said lead wires, i.e., the portion extending between the stem press seal and the base t rminal, is usually constituted by proportioning and composition, to melt more easily than the other lead wire and thereby serve as a fuse upon flow of an abnormally high current therethrough.

Toward the end of lamp life, when the filament fails during operation of the lamp, an arc may be formed, thereby resulting in increased current flow which causes the fuse lead wire to be blown or ruptured. The rupturing of the fuse may cause spattering of molten metal and metallic vapor throughout the stem tube and base with resultant violent arcing and likelihood of damage to the lamp and to the socket in which the lamp is mounted. While various solutions have been proposed, it has been the practice to slip a woven glass or asbestos-paper sleeve over the fuse lead in certain cases to prevent such spattering of the fuse metal. Inserting the sleeve is an expensive manual operation in an otherwise often highly automated manufacture.

It is there-fore an object of the invention to provide a structure and method of assembly which is highly effective in preventing arc damage and which is relatively inexpensive and is adaptable to automatic processing.

The novel features of the invention will appear from the following description taken in conjunction with the drawing wherein:'

FIG. 1 is an elevation, partly in section, of an incandescent lamp comprising the invention; and

FIG. 2 is an elevation, in section and on an enlarged scale, of a base prior to assembly with the lamp bulb.

Referring to FIG. 1 of the drawing, the lamp illustrated therein comprises a glass bulb 1 having a neck portion 2 to which is sealed the upper flared end of a reentrant glass stem tube 3 which has its inner or lower end closed by a press seal portion 4 from which extends a glass arbor 5. A glass exhaust tube 6 extends concentrically through the interior of the stem tube 3 and has its inner end fused in the mass of glass constituting the press seal 4 and is in communication with the interior of the bulb 1 by way of an aperture 7 in said mass of glass. The coiled tungsten wire filment 8 is mounted on and connected to the inner ends of lead wires 9 and 10 which have intermediate portions thereof sealed and embedded in the press seal 4, and outer end portions extending longitudinally through the interior of the stem tube 3. The inner ends of lead wires 9 and 10 may be braced by tie wires 11 and 12 each having one end embedded in the end of the arbor 5.

Attached to the end of the bulb neck 2 is a base 14 which is illustrated as a conventional screw threaded type comprising a threaded sheet metal shell 15 closed at one ice end by a web 16 of insulating material such as molded glass or organic thermosetting plastic and carrying a metallic eyelet 17. The base 14 is secured to the bulb neck by a heat curable cement 18; suitable cement compositions are well known as disclosed, for example, in Patents 2,722,522, Simonelli and 2,633,457, HardWic-k. The outer end of lead wire 9 is bent over the bulb neck 2 and is soldered or welded to the edge of the base shell 15, and the outer end of the other lead wire 10 is threaded through the eyelet 17 and soldered thereto. The outer end portion of one of the lead wires 9 or 10, i.e., the portion extending outwardly from the press seal 4, is usually of copper, and the corresponding portion of the other lead wire is made to melt more easily to serve as a fuse, usually by forming it of a reduced cross section wire of nickel or a copper-silicon alloy.

As thus far described, the lamp is of conventional type. However, in accordance with the invention, destructive arcing is virtually eliminated by filling the interior of the stern tube 3 with a finely divided, dense, insulating ma terial 19 such as dry silica sand or glass beads, and by filling the interior of the base 14 with an insulating resinous foam 20. Tests have'shown that in this manner the lamp is protected from explosion and base damage to a degree unmatched by any other means 'of which We are aware, even at triple over voltage,

The manufacture of the lamp may be conventional except for two steps which are compatible with ordinary automatic lamp processing techniques. The first step is to pour the sand 19 into the stem tube 3 while the lamp bulb assembly is held in a neck-up position prior to placement of the base .14 thereon. The other step, illustrated in FIG. 2, is to place inside the base 14, prior to application of the ring of cement 18, a ring 20a of compressed particles of the foam forming resin mixture. The base may then be handled in a normal manner, the ring 20a being retained therein by an adhesive or by the cement ring 18. That is, with the bulb 1 disposed vertically and neck uppermost, as in FIG. 1, and with the outer end of lead wire 10 extending vertically upward and the outer end of lead wire 9 bent down around the end of the bulb neck 2, the base 14 is brought down on the bulb neck with the lead wire 10 threaded through the eyelet 17. The base is then heated, usually by application of gas flames to the outer surface of the shell 18, to a temperature sufficient to cure the cement 18, for example, about 200 C. The heat of the basing fires also causes the resinous mixture of ring 20a to expand into a porous, brittle, plastic foam filling the base 14. The lamp is then completed, as usual, by trimming the outer ends of the lead wires 9 and 10 and soldering or welding them to the shell 15 and eyelet 17 respectively.

The foam forming mixture may consist essentially of an incompletely condensed phenolic and dolomite (marble flour), for example, a mixture of phenol formaldehyde, hexamethylenetetramine, and one or more fillers or blowing agents such as calcium carbonate, wood flour, gypsum and other insulating materials which further the formation of foam. More particularly, the mixture may consist of, by weight, 5 parts phenol formaldehyde, 1 part hexamethylenetetramine, 8 parts marble flour (magnesium-calcium carbonate), and 0.5 part wood flour. Good results have been obtained with a mixture of 600 grams phenol formaldehyde, grams hexamethylenetetramine, 400 grams marble flour, 48 grams Wood flour and 82 grams talc powder. A simplified formula giving good results consists of 250 grams phenolic resin marketed under the designation GE-13,139 (already containing the hexamethylenetetramine), 139 grams marble flour and 28 grams talc. The powders are mixed and pressed into rings at pressures of 20,000 to 30,000 pounds per square inch. For a standard medium screw base, rings may be made of the latter composition weighing one gram and pressed at 20,000 pounds per square inch into a ring of inch inside diameter and inch outside diameter. However, the rings may have some shape other than cylindrical, so as' to conform more closely to the internal contour of a given base geometry.

Tests have shown that lamps made in accordance with the invention and having the stem tube filled with said, or with glass beads of about 0.5 millimeter diameter, and the base filled with phenolic resin foam, are more positively protected against arcing damage than prior art structures such as those with the woven glass or asbestospaper sleeves. There is apparently an interdependence of base protection and stem protection in achieving complete prevention of violent failures. This was shown by tests of lamps omitting either the base filling of phenolic foam or the steam filling of sand or glass beads which was, in that case, held in the stem tube by a suitable adhesive such as a small amount of epoxy resin.

It will be evident that the filling of the stem 3 with a measured quantity-of sand or glass beads prior to application of the base 14 to the bulb neck, together with loading of the phenolic ring 20a into the base before filling the base with the cement 18, provide an economical and practical system for application to automatic equipment while providing virtually complete protection against violent lamp failures due to arcing.

What we claim as new and desire to secure by Letters Patent of the United States is:

1. An electric incandescent lamp comprising a glass bulb having a neck portion, a reentrant glass stem tube sealed atits outer end to said bulb neck portion and closed at its inner end by a press seal, a filament in said bulb, a pair of lead-in wires electrically connected to respective ends of said filament and extending through said press seal and longitudinally through the interior of said stem tube in spaced relationship, a hollow shell base secured to said bulb neck and carrying contact terminals, said lead-in wires connected to respective said terminals, finely divided insulating material filling the interior of said stem tube, and insulating plastic foam filling the interior of said base.

2. A lamp as set forth in claim 1 wherein said finely divided insulating material is silica sand.

3. A lamp as set forth in claim 1 wherein said finely divided insulating material is glass beads.

References Cited by the Examiner UNITED STATES PATENTS 2,406,271 8/1946 Van Horn 313-318 2,799,795 7/1957 Dickson 3 l33 18 2,922,216 l/ 1960 McIllvaine 2925.l3 3,077,022 2/ 1963 Cullis 2925.l3

JOHN W. HUCKERT, Primary Examiner. I

JAMES D. KALLAM, Examiner.

L. ZALMAN, Assistant Examiner. 

1. AN ELECTRIC INCANDESCENT LAMP COMPRISING A GLASS BULB HAVING A NECK PORTION, A REETRANT GLASS STEM TUBE SEALED AT ITS OUTER END TO SAID BULB NECK PORTION AND CLOSED AT ITS INNER END BY A PRESS SEAL, A FILAMENT IN SAID BULB, A PAIR OF LEAD-IN WIRES ELECTRICALLY CONNECTED TO RESPECTIVE ENDS OF SAID FILAMENT AND EXTENDING THROUGH SAID PRESS SEAL AND LONGITUDINALLY THROUGH THE INTERIOR OF SAID STEM TUBE IN SPACED RELATIONSHIP, A HOLLOW SHELL BASE SE- 